At present, a 3rd Generation Partnership Project (GPP) system generally supports the following duplex modes:
1. Frequency Division Duplex (FDD): a downlink timeslot is transmitted over a downlink carrier and an uplink timeslot is transmitted over an uplink carrier, both of which are paired in an FDD spectrum, and a base station and a mobile terminal can receive and transmit data concurrently;
2. Time Division Duplex (TDD): uplink and downlink timeslots are transmitted in time division over the same TDD carrier; and
3. Half-duplex FDD: a downlink timeslot is transmitted over a downlink carrier and an uplink timeslot is transmitted over an uplink carrier, both of which are paired in an FDD spectrum, and transmission and reception occurs in time division instead of occurring concurrently.
Particularly a frame structure of Long Term Evolution (LTE) FDD is as illustrated in FIG. 1, and a frame structure of LTE TDD is as illustrated in FIG. 2. In FIG. 1 and FIG. 2, a frame has a duration of time of Tf=207200Ts=10 ms and includes 10 sub-frames, each of which is equivalent to a Transmission Time Interval (TTI) with the duration of time of 1 ms, and a sub-frame includes two time slots, each of which has a duration of time of 15360Ts, =0.5 ms.
The 3GPP currently supports beam-forming (i.e., supports an operation mode with a single-antenna port) in which a signal is demodulated with a dedicated pilot of the port 5. For beam-forming, a transmitter can properly transmit a signal only if it knows status information of a channel. In an FDD system, uplink and downlink channels can not be interchangeable due to their different carrier frequencies. That is, a base station can not estimate, status information of a corresponding channel of a downlink carrier frequency, from a Sounding Reference Signal (SRS) transmitted at an uplink carrier frequency from a mobile terminal; and alike, the mobile terminal can not estimate, status information of a corresponding channel of the uplink carrier frequency, from an SRS transmitted at the downlink carrier frequency from the base station. Regardless of whether the mobile terminal or the base station, the ability to acquire current channel statuses of the respective channels relatively accurately is indispensable to controlling of signal transmission and reception.
Therefore a mobile communication system, in which the technical features of the existing FDD system and TDD system at present are integrated, and a corresponding future mobile terminal with an additional function as compared with the existing mobile terminal, will emerge in the future. When the existing mobile terminal and the future mobile terminal are used concurrently in the future mobile communication system, the existing mobile terminal may not operate normally, that is, such a problem may arise that the existing mobile terminal and the future mobile terminal can not be compatible in the future mobile communication system.